The present invention relates to a method of detecting pulse wave, a method of detecting an artery position, and a pulse wave detecting apparatus, which enable a stable detection of the pulse wave irrespective of the operational level of an operator and are suitable for detecting a pulse waveform according to blood flow through an artery or blood vessels around the artery.
As one of the pulse wave detecting apparatuses, a device which detects the pulse wave of a radial artery is known. This device detects changes in pressure to the skin near the radial artery using a pressure sensor, thereby measuring the pulse wave. Since the device detects the change in the pressure applied to the sensor which is placed on the skin above the radial artery, a pressing force of 30 mmHg to 80 mmHg is required in order to stably detect the pulse wave. This causes a strong constrictive feeling in the subject.
For example, in U.S. Pat. No. 4,951,679, a pressure sensor placed near the radial artery is pressed against the arm while varying the pressing force in sequence to detect the pressing force with the maximum amplitude of a detected signal. The pulse wave is detected with this pressing force. This allows an optimum pressing force to be set without applying unnecessary pressure. However, it is necessary to apply a predetermined pressure against the arm, thereby leaving the problem of a strong constrictive feeling.
On the contrary, some pulse wave detecting apparatuses utilizing ultrasound or light (such as infrared radiation and laser beams) do not require a strong pressing force. In a pulse wave detecting apparatus which uses a reflected wave of ultrasound, a probe that emits ultrasound is applied to the arm of a subject from the outer side and the probe receives the ultrasound reflected by an artery or the like to measure the pulse wave.
On the other hand, a pulse wave detecting apparatus which uses light emits a light from a light emitting diode, for example, to the inside of a body to detect the amount of reflected light (reflected light from subcutaneous tissues). Since part of the light emitted from the light emitting diode is absorbed by hemoglobin in the blood vessels, the amount of reflected light is related to blood capacity in the blood vessels to be detected as the pulse wave.
In a conventional pulse wave detecting apparatus using ultrasound, the detected values of the reflected wave vary in accordance with angles between a probe which transmits and receives ultrasound and blood flow. In the operation of the probe, it is difficult to maintain a fixed angle to the blood flow, thereby causing difficulty in stable measurement of the pulse wave. For example, in the case where the probe is applied to the palm side of a subject""s arm, the detection of the pulse wave becomes difficult if the probe shifts only by several millimeters from an artery. In the case where the probe is applied to the backhand side of the subject""s arm, a signal-to-noise (SN) ratio necessary for detecting the pulse wave can not be secured.
In a device utilizing a laser or light-emitting diode, if irradiating light is not applied to the artery, the SN ratio necessary for detecting the pulse waveform can not be secured or stable pulse waveform can not be detected.
Conventionally, the pulse waveform has been detected based on the blood flowing in the artery. According to traditional Oriental medicine, it is believed that the conditions of a living body can be monitored based on the pulse waveform. The artery formed of smooth muscles and the like supplies blood to the peripheral tissues by the pulsation. Since the artery is a tissue of the living body, it is necessary to provide the artery with blood. The arteriole supplies blood to the arterial tissues. Since the arteriole supplies blood to the artery itself, the condition of the artery can be monitored by detecting the pulse waveform based on the blood flow of the arteriole. However, in conventional methods for detecting pulse waves, the pulse waveform has been detected based on the blood flowing in the artery, but the pulse waveform based on blood flowing in the arteriole has not been detected.
The present invention has been achieved to solve the above-described problems. An object of the present invention is to provide a method of detecting a pulse wave, a method of detecting an artery position, and a pulse wave detecting apparatus, which enable stable detection of the pulse wave independent of the skill level of an operator without forcing a strong constrictive feeling on the subject, and are suitable for detecting the pulse waveform according to blood flow through an artery or blood vessels around the artery.
(1) A method of detecting a pulse wave according to the present invention, uses a pulse wave detection means which detects a pulse waveform of blood flowing through blood vessels around an artery, and the method comprises steps of:
detecting the pulse waveform by the pulse wave detection means at a plurality of positions;
sensing a polarity of the pulse waveform detected by the pulse wave detection means; and
detecting the pulse waveform detected in a position range from a position where the polarity is inverted to a position where the polarity is returned to an original polarity as the pulse waveform from the blood vessels around the artery.
According to the present invention, the polarity of the pulse waveform in the blood vessels around an artery is sensed, the pulse waveform being detected at a plurality of positions and the pulse waveform in the blood vessels around the artery are detected in a position range from a position where the polarity is inverted to a position where the polarity is returned to the original polarity, that is, in the position range in which the polarity inversion resulting from the compression due to the artery is observed. This allows the pulse waveform from blood flowing through the arteriole, which is the blood vessel surrounding the artery, to be reliably detected with a high signal-to-noise ratio.
(2) A method of detecting a pulse wave according to the present invention, comprises steps of:
detecting a pulse waveform by a pulse wave detection means which detects the pulse waveform from blood flowing through blood vessels around an artery at a plurality of detection positions;
sensing a polarity of the pulse waveform detected by the pulse wave detection means; and
detecting the pulse wave of the artery positioned approximately at a center of the blood vessels around the artery in a position range from a position where the polarity is inverted to a position where the polarity is returned to an original polarity.
According to the present invention, the polarity of the pulse waveform in the blood vessels around an artery is sensed, the pulse waveform being detected at a plurality of positions and the pulse waveform in the artery positioned approximately at the center of the blood vessels around the artery are detected in a position range from a position where the polarity is inverted to a position where the polarity is returned to the original polarity, that is, in the position range in which the polarity inversion resulting from the compression due to the artery is observed. This allows the pulse wave of the artery to be detected at the accurately specified position, so that the pulse waveform of the artery can be reliably detected with a high signal-to-noise ratio.
(3) A method of detecting a position of an artery according to the present invention, using a pulse wave detection means which detects a pulse waveform of blood flowing through blood vessels around the artery, comprises the steps of:
detecting the pulse waveform by the pulse wave detection means at a plurality of positions;
sensing a polarity of the pulse waveform detected by the pulse wave detection means; and
detecting the location of the artery in a position range from a position where the polarity is inverted or is in the process of being inverted to a position where the polarity is returned to an original polarity.
According to the present invention, the polarity of the pulse waveform of the blood vessels around an artery is sensed, the pulse waveform being detected at a plurality of positions and the location of the artery is detected in a position range from a position where the polarity is inverted or is in the process of being inverted to a position where the polarity is returned to the original polarity, that is, in the position range in which the polarity inversion or its process of inversion resulting from the compression due to the artery is observed. This allows the position of the artery positioned approximately at the center of arterioles adjacent to and surrounding the artery to be reliably detected.
(4) A pulse wave detecting apparatus according to the present invention comprises:
a pulse wave detection means for detecting a pulse waveform of blood vessels around an artery from a detection part of a living body at a plurality of positions; and
a pulse wave waveform display means for displaying the pulse waveform.
According to the present invention, the pulse waveform of the blood vessels around an artery at a plurality of positions which has been detected by the pulse wave detection means can be monitored through the pulse waveform display means. Therefore, the pulse waveform from the arterioles adjoining the periphery of the artery can be easily detected by recognizing the polarity inversion of the pulse waveform.
(5) A pulse wave detecting apparatus according to the present invention comprises:
a pulse wave detection means for detecting a pulse waveform of blood vessels around an artery from a detection part of a living body at a plurality of positions;
a polarity detection means for detecting a polarity of the pulse waveform which is output from the pulse wave detection means; and
an announcement means for announcing a detection result of the polarity detection means.
According to the present invention, the polarity, detected by the polarity detection means can be monitored through the announcement means, for the pulse waveform of the blood vessels around the artery at a plurality of positions detected by the pulse wave detection means. Therefore, the polarity inversion of the pulse waveform can be easily recognized so that the pulse waveform from the arterioles adjoining around the artery can be reliably detected.
(6) In the pulse wave detecting apparatus described above, it is preferable to further comprise a position change means for changing a relative position between the pulse wave detection means and the detection part.
According to the present invention, the pulse waveform of the blood vessels around the artery can easily be detected at a plurality of positions by changing the relative position between the pulse wave detection means and the detection part by the position change means.
(7) In the pulse wave detecting apparatus described above, it is preferable that the position change means changes the relative position between the pulse wave detection means and the detection part so as to exist within a position range from a position where the polarity detected by the polarity detection means is inverted to a position where the polarity is returned to the original polarity.
According to the present invention, the position change means changes the relative position between the pulse wave detection means and the detection part so as to locate within a position range from a position where the polarity is inverted to a position where the polarity is returned to the original polarity, that is, within the position range where the polarity inversion resulting from the compression due to the artery is observed. Therefore, the pulse wave detection means allows the pulse waveform from blood flowing through the arterioles, which are the blood vessels surrounding the artery, to be reliably detected with a high signal-to-noise ratio.
(8) In the pulse wave detecting apparatus described above, it is preferable that the apparatus further comprise a body movement elimination means for eliminating a component due to body movement from the pulse waveform detected by the pulse wave detection means to create a body movement eliminated pulse waveform, and the polarity detection means detects a polarity based on the body movement eliminated pulse waveform.
According to the present invention, the polarity detection means detects the polarity based on the body movement eliminated pulse waveform in which the component due to the body movement have been eliminated by the body movement elimination means. Therefore, the polarity detection means can detect the polarity reliably even if there are body movements.
(9) The pulse wave detecting apparatus according to the present invention comprises:
a pulse wave detection means for detecting a pulse waveform of blood vessels around an artery from a detection part of a living body at a plurality of positions;
a polarity detection means for detecting a polarity of the pulse waveform which is output from the pulse wave detection means;
an amplitude detection means for detecting an amplitude of the pulse waveform which is output from the pulse wave detection means; and
an announcement means for announcing a detected result of the polarity detection means and a detected result of the amplitude detection means.
According to the present invention, the polarity detected by the polarity detection means and the amplitude of the pulse waveform detected by the amplitude detection means for the pulse waveform of the blood vessels around the artery at a plurality of positions detected by the pulse wave detection means can be monitored through the announcement means. Therefore, the polarity inversion and the amplitude change of the pulse waveform can easily be recognized so that the pulse waveform from the arteriole adjoining around the artery can be reliably detected with a high signal-to-noise ratio.
(10) The pulse wave detecting apparatus according to the present invention comprises:
a pulse wave detection means for detecting a pulse waveform of blood vessels around an artery from a detection part of a living body at a plurality of positions;
a polarity detection means for detecting a polarity of the pulse waveform which is output from the pulse wave detection means; and
a position change means for changing the relative position between of the pulse wave detection means and the detection part approximately to a center position in a position range from a position where the polarity detected by the polarity detection means is inverted to a position where the polarity is returned to the original polarity.
According to the present invention, the position change means changes the relative position between the pulse wave detection means and the detection part to the center position in the position range from a position where the polarity is inverted to a position where the polarity is returned to the original polarity, that is, to the center position in the position range where the polarity inversion resulted from the compression due to the artery is observed based on the polarity detected by the polarity detection means for the pulse waveform of the blood vessels around the artery at a plurality of positions detected by the pulse wave detection means. Therefore, the pulse wave detection means can reliably detect with a high signal-to-noise ratio the pulse waveform from blood flowing through arterioles surrounding the circumference of the artery.
(11) The pulse wave detecting apparatus according to the present invention comprises:
a pulse wave detection means for detecting a pulse waveform of blood vessels around an artery from a detection part of a living body at a plurality of positions;
a polarity detection means for detecting a polarity of the pulse waveform which is output from the pulse wave detection means;
an amplitude detection means for detecting an amplitude of the pulse waveform which is output from the pulse wave detection means; and
a position change means for changing the relative position between the pulse wave detection means and the detection part so that the relative position resides in a position range from a position where the polarity detected by the polarity detection means is inverted to a position where the polarity is returned to an original polarity and the amplitude detected by the amplitude detection means is made substantially maximized.
According to the present invention, the position change means changes the relative position between the pulse wave detection means and the detection part so that the relative position resides in the position range from a position where the polarity is inverted to a position where the polarity is returned to the original polarity, that is, in the position range where the polarity inversion resulting from the compression due to the artery is observed and the amplitude detected by the amplitude detection means is made a maximum based on the polarity detected by the polarity detection means for the pulse waveform of the blood vessels around the artery at a plurality of positions detected by the pulse wave detection means. Therefore, the pulse wave detection means can reliably detect with a high signal-to-noise ratio the pulse waveform from the blood flow flowing through arterioles surrounding the periphery of the artery.
(12) In the pulse wave detecting apparatus described above, it is preferable to comprise a body movement elimination means for eliminating a component due to a body movement from the pulse waveform detected by the pulse wave detection means to create a body movement eliminated pulse wave waveform,
wherein the polarity detection means detects a polarity based on the body movement eliminated pulse wave waveform, and
wherein the amplitude detection means detects an amplitude based on the body movement eliminated pulse wave waveform.
According to the present invention, the polarity detection means detects the polarity and the amplitude detection means detects the amplitude based on the body movement eliminated pulse waveform in which the component due to the body movement is eliminated from the pulse waveform by the body movement elimination means. Therefore, even if there are body movements, the polarity detection means can properly detect the polarity and the amplitude detection means can accurately detect the amplitude.
(13) In the pulse wave detecting apparatus described above, it is preferable that the body movement elimination means comprises a body movement detection section for detecting the body movement of the living body, a first frequency analysis section for performing a frequency analysis of a body movement waveform detected by the body movement detection section, a second frequency analysis section for performing a frequency analysis of a pulse waveform detected by the pulse wave detection means, and a body movement elimination section creating the body movement eliminated pulse waveform by comparing frequency analysis results analyzed by the first frequency analysis section and the second frequency analysis section.
According to the present invention, frequency analysis of the body movement waveform detected by the body movement detection section is performed by the first frequency analysis section, and frequency analysis of the pulse waveform detected by the pulse wave detection means is performed by the second frequency analysis section, so that the body movement elimination section can accurately create the body movement eliminated pulse wave waveform by comparison of those analysis results.
(14) In the pulse wave detecting apparatus described above, it is preferable that the first and second frequency analysis sections perform frequency analysis using FFT.
(15) In the pulse wave detecting apparatus described above, it is preferable that the position change means move while stopping for a discontinuance time which is at least a minimum period of time to perform the FFT.
According to the present invention, the FFT can be properly performed at each position changed by the position change means.
(16) In the pulse wave detecting apparatus described above, it is preferable that the first and second frequency analysis sections perform frequency analysis using wavelet transformation.
(17) In the pulse wave detecting apparatus described above, it is preferable that the position change means moves while stopping for a discontinuance time which is at least a minimum period of time to perform the wavelet transformation.
According to the present invention, the wavelet transformation can be properly performed at each position changed by the position change means.
(18) In the pulse wave detecting apparatus described above, it is preferable that the body movement elimination means comprises:
a frequency analysis section for performing frequency analysis of the pulse waveform from the pulse wave detection means; and
a body movement separation section creating the body movement eliminated pulse waveform based on a frequency component from which a low frequency component is eliminated in a frequency analysis result analyzed by the frequency analysis section.
According to the present invention, the body movement separation section eliminates a low frequency component from the frequency analysis result analyzed by the frequency analysis section, so that the body movement elimination means can create the body movement eliminated pulse waveform from which a component due to the body movement, having a high probability of existing in a lower frequency range than a basic frequency component of the pulse waveform, are substantially eliminated. Therefore, the present invention can create the body movement eliminated pulse waveform with a simple configuration without using the body movement detection section and the first frequency analysis section required by the body movement elimination means described above.
(19) In the pulse wave detecting apparatus described above, it is preferable that the body movement separation section determine the maximum frequency of the low frequency component based on a basic frequency of the pulse waveform detected by the pulse wave detection means.
According to the present invention, in the body movement separation section, it is noticed that when the pulse is increased by exercise or the like, the consequent frequency of the basic component of the pulse waveform rises and the frequency component of the body movement is also increased, since the body is active during exercise. Therefore, the maximum frequency of the low component to be eliminated is determined based on the basic frequencies of the pulse waveform detected by the pulse wave detection means. This allows body movement component to be eliminated with a high probability even if the frequencies of component due to the body movements by exercise or the like are increased.
(20) In the pulse wave detecting apparatus described above, it is preferable that the frequency analysis section perform frequency analysis using FFT or wavelet transformation.
(21) In the pulse wave detecting apparatus"" described above, it is preferable that the pulse wave detection means be an optical type pulse wave detection means detecting a pulse wave of blood vessels around an artery based on a light absorption property of blood flowing through the blood vessels around the artery.
According to the present invention, a pressing force is not required to be applied to the detection part as with a pulse wave detection means of the compression sensor type since a pulse wave detection means of the optical type is used. Thus, pulse wave can be detected without causing a constrictive feeling to a subject, and the pulse wave detection means can be easily moved in order to detect the pulse wave at a plurality of positions.
(22) In the pulse wave detecting apparatus described above, it is preferable that the pulse wave detection means be set so that a detection wavelength exists in a wavelength range from 300 nm to 700 nm.
According to the present invention, the detected wavelength of the optical type pulse wave detection means is set in the wavelength range from 300 nm to 700 nm, the absorption ratio of the wavelength range is high due to the hemoglobin in the blood, so that the absorbed amount of light detected by the pulse wave detection means greatly varies according to the amount of blood in the blood vessels. Accordingly, the pulse waveform can be detected accurately.
In addition, as the light with a wavelength below 700 nm is difficult to transmit through the tissue of a living body, pulse wave from blood vessels around an artery, which blood vessels exist in an area shallower than the artery, can be detected and are free from the influence of the outside light.
(23) In the pulse wave detecting apparatus described above, it is preferable to further comprise an artery pulse wave detection means for detecting a pulse wave of an artery positioned approximately at a center of blood vessels around the artery, and
wherein the artery pulse wave detection means is provided substantially at the same position as the pulse wave detection means and the relative position between the artery pulse wave detection means and the detection part is changed by the position change means.
According to the present invention, the artery pulse wave detection means for detecting pulse wave of an artery positioned approximately at the center of the blood vessels around the artery is provided substantially at the same position as the pulse wave detection means, and the relative position between the artery pulse wave detection means and the detection part is changed by the position change means. Accordingly, when the pulse wave detection means is moved by the position change means to a position at which the pulse waveform of arterioles positioned around the artery is to be measured, the artery pulse wave detection means can accurately detect the pulse wave of the artery positioned approximately at the center of the arterioles.